Basic XPS Information Section

The Basic XPS Information Section provides fundamental XPS spectra, BE values, FWHM values, BE tables, overlays of key spectra, histograms and a table of XPS parameters.
The Advanced XPS Information Section is a collection of additional spectra, overlays of spectra, peak-fit advice, data collection guidance, material info,
common contaminants, degradation during analysis, auto-oxidation, gas capture study, valence band spectra, Auger spectra, and more.
Published literature references, and website links are summarized at the end of the advanced section.

→  Periodic Table – HomePage                   XPS Database of Polymers               → Six (6) BE Tables

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Potassium (K)

Kalium

Challacolloite – KPb2Cl5	Potassium Metal – Ko	Sylvite – KCl

 

Page Index
Pure Element Spectra with Peak-fits IMFP and Cross-sections for Pure Element Native Oxide Spectra with Peak-fits Pure Oxide Spectra with Peak-fits	Valence Band Spectra Six (6) Tables of Chemical State BEs Histograms of NIST BEs Advanced XPS Information Section	Peak-fits and Overlays of Rb Chemical Compounds	Auger Peaks and Spectra Contamination XPS Facts, Guidance, Information Chemical State Spectra from Literature

• Expert Knowledge & Explanations

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Potassium (K^o) Metal

Peak-fits, BEs, FWHMs, and Peak Labels

 

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Potassium Metal (Ko) K (2p) Spectrum – raw Ion etched clean Flood Gun OFF – conductive metal	Potassium Metal (Ko) K (2p) Spectrum – peak-fit Ion etched clean Flood Gun OFF – conductive metal
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Potassium Metal (Ko) K (2p) extended range Ion etched clean Flood Gun OFF – conductive metal	Potassium Metal (Ko) K (2s) Spectrum – peak-fit Ion etched clean Flood Gun OFF – conductive metal
Survey Spectrum of Potassium (Ko) Metal with Peaks Integrated, Assigned and Labelled
→  Periodic Table   XPS Signals for Potassium, (Ko) Metal Spin-Orbit Term,  BE (eV) Value, and Scofield σ for Potassium Kα X-rays (1486 eV, 8.33 Ang) Overlaps Spin-Orbit Term BE (eV) Value Scofield σ from 1486 eV X-rays IMFP (TPP-2M) in Å K (2s) 389 2.27 59.1 K (2p1/2) 296.88 1.35 62.6 C (1s) C-F overlaps K (2p3/2) 294.07 2.62 73.7 K (3s) 41 0.286 73.7 O (2s) overlaps K (3p ) 25 0.362 74.4 σ:  abbreviation for the term Scofield Photoionization Cross-Section which are used with IMFP and TF to produce RSFs and atom% quantitation Plasmon Peaks Energy Loss Peaks Auger Peaks Energy Loss Peak for Compounds:  ~xx eV above each peak max Intrinsic Bulk Plasmon Peaks:  ~x eV steps Expected Bandgap for KF: ~  6-6.5 eV    *Scofield Cross-Section (σ) for C (1s) = 1.0 →  Periodic Table
Plasmon Peaks from Ko Metal Fresh exposed bulk produced by extensive Ar+ ion etching

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K (2p) – Extended Range Spectrum	K (2p) – Extended Range Spectrum – Vertically Expanded

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K (KLL) Auger Peaks from K^o Metal
Fresh exposed bulk produced by extensive Ar+ ion etching

Ko Metal – High resolution Auger peaks	Ko Metal – same Auger peaks but taken from Survey spectrum

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Side-by-Side Comparison of

Potassium (K) and Potassium Halides
Peak-fits, BEs, FWHMs, and Peak Labels

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Pure Metal, Ko	Potassium Fluoride, KF
K (2p) from Potassium metal – raw Ion Etched	Peak-fit of K (2p) from KF freshly cleaved in lab air Charge Referenced to 285.0 eV

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Potassium Fluoride, KF Peak-fit of K (2p) from KF freshly cleaved in lab air Charge Referenced to 285.0 eV	Potassium Chloride, KCl Peak-fit of K (2p) from KCl, xtal freshly cleaved in lab air Charge Referenced to 285.0 eV

	.
Potassium Bromide, KBr Peak-fit of K (2p) from KBr, xtal freshly cleaved in lab air Charge Referenced to 285.0 eV	Potassium Iodide, KI Peak-fit of K (2p) from KI xtal freshly cleaved in lab air Charge Referenced to 285.0 eV

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Overlay of K (2p) Peak
from Potassium, K^o, KF, and KI

 

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Survey Spectrum of Potassium Fluoride, KF
with Peaks Integrated, Assigned and Labelled

 

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Survey Spectrum of Potassium Chloride, KCl
with Peaks Integrated, Assigned and Labelled

 

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Survey Spectrum of Potassium Bromide, KBr
with Peaks Integrated, Assigned and Labelled

 

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Survey Spectrum of Potassium Iodide, KI
with Peaks Integrated, Assigned and Labelled

 

 

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Overlay Study of
Carbonate and Bi-Carbonate Chemical Groups

Overlay of C (1s) Spectra from K₂CO₃ and KHCO₃

Potassium Carbonate, K2CO3 Peak-fit of C (1s) from K2CO3, powder pressed onto stage Charge Referenced to 285.0 eV	Potassium Hydrogen Carbonate, KHCO3   (potassium bi-carbonate) Peak-fit of C (1s) from KHCO3, crystallites freshly crushed Charge Referenced to 285.0 eV
Overlay of C (1s) Spectra from K2CO3 and KHCO3
Overlay of K (2p) Spectra  from K2CO3 and KHCO3
Potassium Carbonate, K2CO3 Peak-fit of K (2p) Spectrum from K2CO3, powder pressed onto stage Charge Referenced to 285.0 eV	Potassium Hydrogen Carbonate, KHCO3 (potassium bi-carbonate) Peak-fit of K (2p) Spectrum from KHCO3, crystallites freshly crushed Charge Referenced to 285.0 eV
Overlay of K (2p) Spectra  from K2CO3 and KHCO3

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Valence Band Spectra

K₂CO₃ and KHCO₃

K2CO3 Valence Band Spectrum	KHCO3 Valence Band Spectrum
Overlay of Valence Band Spectra K2CO3 and KHCO3
Expanded View of Valence Band Spectra

 

Features Observed

• xx
• xx
• xx

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Valence Band Spectra

KF, KCl, KBr, KI

KF Valence Band Spectrum	KCl Valence Band Spectrum
	.
KBr Valence Band Spectrum	KI Valence Band Spectrum
Overlay of Valence Band Spectra KF, KCl, KBr and KI

 

 

Copyright ©:  The XPS Library

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Potassium Minerals, Gemstones, and Chemical Compounds
Carnallite – KMgCl3 · 6H2O	Saltonseaite – K3NaMnCl6	Kainite – KMg(SO4)Cl · 3H2O	Chlorothionite – K2Cu(SO4)Cl2

→  Periodic Table 

 

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Six (6) Chemical State Tables of K (2p) BEs

 

• The XPS Library Spectra-Base
• PHI Handbook
• Thermo-Scientific Website
• XPSfitting Website
• Techdb Website
• NIST Website

 

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Notes of Caution when using Published BEs and BE Tables from Insulators and Conductors:

• Accuracy of Published BEs
  • The accuracy depends on the calibration BEs used to calibrate the energy scale of the instrument.  Cu (2p_3/2) BE can vary from 932.2 to 932.8 eV for old publications
  • Different authors use different BEs for the C (1s) BE of the hydrocarbons found in adventitious carbon that appears on all materials and samples.  From 284.2 to 285.3 eV
  • The accuracy depends on when the authors last checked or adjusted their energy scale to produce the expected calibration BEs
• Worldwide Differences in Energy Scale Calibrations
  • For various reasons authors still use older energy scale calibrations
  • Some authors still adjust their energy scale so Cu (2p_3/2) appears at 932.2 eV or 932.8 eV because this is what the maker taught them
  • This range causes BEs in the higher BE end to be larger than expected
  • This variation increases significantly above 600 eV BE
• Charge Compensation
  • Samples that behave as true insulators normally require the use of a charge neutralizer (electron flood gun with or without Ar+ ions) so that the measured chemical state spectra can be produced without peak-shape distortions or sloping tails on the low BE side of the peak envelop.
  • Floating all samples (conductive, semi-conductive, and non-conductive) and always using the electron flood gun is considered to produce more reliable BEs and is recommended.
• Charge Referencing Methods for Insulators
  • Charge referencing is a common method, but it can produce results that are less reliable.
  • When an electron flood gun is used, the BE scale will usually shift to lower BE values by 0.01 to 5.0 eV depending on your voltage setting. Normally, to correct for this flood gun induced shift, the BE of the hydrocarbon C (1s) peak maximum from adventitious carbon is used to correct for the charge induced shift.
  • The hydrocarbon peak is normally the largest peak at the lowest BE.
  • Depending on your preference or training, the C (1s) BE assigned to this hydrocarbon peak varies from 284.8 to 285.0 eV.  Other BEs can be as low as 284.2 eV or as high as 285.3 eV
  • Native oxides that still show the pure metal can suffer differential charging that causes the C (1s) and the O (1s) and the Metal Oxide BE to be larger
  • When using the electron flood gun, the instrument operator should adjust the voltage and the XY position of the electron flood gun to produce peaks from a strong XPS signal (eg O (1s) or C (1s) having the most narrow FWHM and the lowest experimentally measured BE.

 →  Periodic Table 

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Table #1

K (2p_3/2) Chemical State BEs from:  “The XPS Library Spectra-Base”

C (1s) BE = 285.0 eV for TXL BEs
and C (1s) BE = 284.8 eV for NIST BEs

Element	Atomic #	Compound	As-Measured by TXL or NIST Average BE	Largest NIST BE	Hydrocarbon C (1s) BE	Source
K	19	K-2Ti4O9	292.4 eV		285.0 eV	The XPS Library
K	19	K-F (N*3)	292.5 eV	293.1 eV		Avg BE – NIST
K	19	K-2O	292.7 eV	292.9 eV	285.0 eV	The XPS Library
K	19	K-ClO4 (N*2)	292.8 eV	293.4 eV		Avg BE – NIST
K	19	K-Cl	292.9 eV		285.0 eV	The XPS Library
K	19	K-Br	293.0 eV		285.0 eV	The XPS Library
K	19	K-2SO4 (N*1)	293.3 eV			Avg BE – NIST
K	19	K-C8 (N*1)	294.4 eV			Avg BE – NIST
K	19	K -element (N*1)	294.7 eV			Avg BE – NIST
K	19	K-CN (N*1)	294.7 eV			Avg BE – NIST
K	19	K-2CO3			285.0 eV	The XPS Library
K	19	K-HCO3			285.0 eV	The XPS Library

 (N*number) identifies the number of NIST BEs that were averaged to produce the BE in the middle column.

• Binding Energy Scale Calibration expects Cu (2p_3/2) BE = 932.62 eV and Au (4f_7/2) BE = 83.98 eV.  BE (eV) Uncertainty Range:  +/- 0.2 eV
• Charge Referencing of insulators is defined such that the Adventitious Hydrocarbon C (1s) BE (eV) = 285.0 eV.  NIST uses C (1s) BE = 284.8 eV 
• Note:   Ion etching removes adventitious carbon, implants Ar (+), changes conductivity of surface, and degrades chemistry of various chemical states.
• Note:  Ion Etching changes BE of C (1s) hydrocarbon peak.
• TXL – abbreviation for: “The XPS Library” (https://xpslibrary.com).  NIST:  National Institute for Science and Technology (in USA)

 →  Periodic Table 

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Table #2

K (2p_3/2) Chemical State BEs from:  “PHI Handbook”

C (1s) BE = 284.8 eV

 

Copyright ©:  Ulvac-PHI

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Table #3

K (2p_3/2) Chemical State BEs from:  “Thermo-Scientific” Website

C (1s) BE = 284.8 eV

Chemical state	Binding energy, K 2p3/2 (eV)
KCl	292.9
KBr	293.2

Copyright ©:  Thermo Scientific website

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Table #4

K (2p_3/2) Chemical State BEs from:  “XPSfitting” Website

Chemical State BE Table derived by Averaging BEs in the NIST XPS database of BEs
C (1s) BE = 284.8 eV

 

Copyright ©:  Mark Beisinger

 

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Table #5

K (2p_3/2) Chemical State BEs from:  “Techdb.podzone.net” Website

 

XPS Spectra – Chemical Shift | Binding Energy
C (1s) BE = 284.6 eV

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Table #6

NIST Database of K (2p_3/2) Binding Energies

NIST Standard Reference Database 20, Version 4.1

Data compiled and evaluated
by
Alexander V. Naumkin, Anna Kraut-Vass, Stephen W. Gaarenstroom, and Cedric J. Powell
©2012 copyright by the U.S. Secretary of Commerce on behalf of the United States of America. All rights reserved.

Important Note:  NIST Database defines Adventitious Hydrocarbon C (1s) BE = 284.8 eV for all insulators.

 

 

 

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Advanced XPS Information Section

 

Spectra, BEs, Features, Guidance and Cautions  

for XPS Research Studies on Potassium Materials

 

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Expert Knowledge Explanations

 

Overlay reveals shift	Shake-up Example	Auger signal overlaps X

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XPS Spectra

from

Common Potassium Compounds

                           

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Potassium Oxide, KO₂  (Super-oxide)
lump, fresh cut

 

Survey Spectrum	K (2p) Chemical State Spectrum
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C (1s) Chemical State Spectrum	O (1s) Chemical State Spectrum
	.
Valence Band Spectrum from KO2	O Auger Spectrum from KO2

 

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Potassium Permanganate, KMnO₄
crystallite, crushed

Survey Spectrum	K (2p) Chemical State Spectrum
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Mn (2p) Chemical State Spectrum	O (1s) Chemical State Spectrum
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C (1s) Chemical State Spectrum	Valence Band Chemical State Spectrum

• xx
• xx
• xx

→  Periodic Table 

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Quantitation Details and Information

Quantitation by XPS is often incorrectly done, in many laboratories, by integrating only the main peak, ignoring the Electron Loss peak, and the satellites that appear as much as 30 eV above the main peak.  By ignoring the electron loss peak and the satellites, the accuracy of the atom% quantitation is in error.

When using theoretically calculated Scofield cross-section values, the data must be corrected for the transmission function effect, use the calculated TPP-2M IMFP values, the pass energy effect on the transmission function, and the peak area used for calculation must include the electron loss peak area, shake-up peak area, multiplet-splitting peak area, and satellites that occur within 30 eV of the main peak.

 

Quantitation from Pure, Homogeneous Binary Compound
composed of KF

This section is focused on measuring and reporting the atom % quantitation that results by using:

• Scofield cross-sections,
• Spectra corrected to be free from Transmission Function effects
• A Pass Energy that does not saturate the detector system in the low KE range (BE = 1000-1400 eV)
• A focused beam of X-ray smaller than the field of view of the lens
• An angle between the lens and the source that is ~55 deg that negates the effects of beta-asymmetry
• TPP-2M inelastic mean free path values, and
• Either a linear background or an iterated Shirley (Sherwood-Proctor) background to define peak areas

The results show here are examples of a method being developed that is expected to improve the “accuracy” or “reliability” of the atom % values produced by XPS.

 

Copyright ©:  The XPS Library  

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XPS Facts, Guidance & Information

→  Periodic Table 

		Element		Potassium (K)
		Primary XPS peak used for Peak-fitting :		K (2p3/2)
		Spin-Orbit (S-O) splitting for Primary Peak:		Spin-Orbit splitting for K (2p) orbital is: 2.9 eV
		Binding Energy (BE) of Primary XPS  Signal:		294 eV
		Scofield Cross-Section (σ) Value:		K (2p3/2) = 2.62     K (2p1/2) = 1.35
		Conductivity:		Potassium Resistivity = xx K2CO3 Resistivity = xx
		Range of K (2p) Chemical State BEs:		294 – 295 eV range   (Ko to KF)
		signals from other elements that overlap K (2p) Primary Peak:		xx
		Bulk Plasmons:		~
		Shake-up Peaks:		xx
		Multiplet Splitting Peaks:		not possible
		General Information about Potassium Compounds:		xx
		Cautions – Chemical Poison Warning		Flammable in water

Copyright ©:  The XPS Library 

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Information Useful for Peak-fitting K (2p_3/2)

• FWHM (eV) of Pure Potassium metal:  0.8 eV using 25 eV Pass Energy after ion etching and very fast data collection cycles
• FWHM (eV) of Potassium Halides:  1.3 eV using 50 eV Pass Energy  (before ion etching)
• Binding Energy (BE) of Primary signal used for Measuring Chemical State Spectra:  294 eV for K (2p) with +/- 0.2 uncertainty
• List of XPS Peaks that can Overlap Peak-fit results for K (2p):  xx

→  Periodic Table 

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General Guidelines for Peak-fitting XPS signals

• Typical Energy Resolution for Pass Energy (PE) setting used to measure Chemical State Spectra on Various XPS Instruments
  • Ag (3d_5/2) FWHM (eV) = ~0.95 eV for PE 50 on Thermo K-Alpha
  • Ag (3d_5/2) FWHM (eV) = ~1.00 eV for PE 80 on Kratos Nova
  • Ag (3d_5/2) FWHM (eV) = ~0.95 eV for PE 45 on PHI VersaProbe
  • Ag (3d_5/2) FWHM (eV) = ~0.85 eV for PE 50 on SSI S-Probe
• FWHM (eV) of Pure Elements: Ranges from 0.4 to 1.0 eV across the periodic table
• FWHM of Chemical State Peaks in any Chemical Compound:  Ranges from 1.1 to 1.6 eV  (in rare cases FWHM can be 1.8 to 2.0 eV)
• FWHM of Pure Element versus FWHM of Metal Oxide:  Pure element FWHM << Metal Oxide FWHM  (e.g. 0.8 vs 1.5 eV, roughly 2x)
• If FWHM Greater than 1.6 eV:  When a peak FWHM is larger than 1.6 eV, it is best to add another peak to the peak-fit envelop.
• BE (eV) Difference in Chemical States: The difference in chemical state BEs is typically 1.0-1.3 eV apart.  In rare cases, <0.8 eV.
• Number of Peaks to Use:  Use minimum. Do not use peaks with FWHM < 1.0 eV unless it is a metal or a conductive compound.
• Typical Peak-Shape:  80% G: 20% L,   1.4 eV Gaussian and 0.5 eV Lorentzian
• Spin-Orbit Splitting of Two Peaks (due to Coupling):  The ratio of the two (2) peak areas must be constrained.
• Constraints used on Peak-fitting: typically constrain the peak area ratios based on the Scofield cross-section values
• Asymmetry for Conductive materials:  20-30% with increased Lorentzian %
• Peak-fitting “2s” or “3s” Peaks:  Often need to use 50-60% Lorentzian peak-shape
• Notes:
  • Other Oxidation States can appear as small peaks when peak-fitting
  • Pure element signals normally have asymmetric tails that should be included in the peak-fit.
  • Gaseous state materials often display asymmetric tails due to vibrational broadening.
  • Peak-fits of C (1s) in polymers include an asymmetric tail when the energy resolution is very high.
  • Binding energy shifts of some compounds are negative due to unusual electron polarization.

→  Periodic Table 

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Contaminants Specific to Potassium Metal

• Potassium metal develops a Native oxide that is usually 8-9 nm thick.  .
• With heat the Native oxide becomes thicker and the BE of the oxide shifts to higher BE
• Potassium does not readily form a carbide when the surface is ion etched inside the analysis chamber

 

Commonplace Contaminants

• Carbon and Oxygen are common contaminants that appear on nearly all surfaces. The amount of Carbon usually depends on handling.
• Carbon is usually the major contaminant.  The amount of carbon ranges from 5-50 atom%.
• Carbon contamination is attributed to air-borne organic gases that become trapped by the surface, oils transferred to the surface from packaging containers, static electricity, or handling of the product in the production environment.
• Carbon contamination is normally a mixture of different chemical states of carbon (hydrocarbon, alcohol or ether, and ester or acid).
• Hydrocarbon is the dominant form of carbon contamination. It is normally 2-4x larger than the other chemical states of carbon.
• Carbonate peaks, if they appear, normally appear ~4.5 eV above the hydrocarbon C (1s) peak max BE.
• Low levels of Carbonate is common on many metals that readily oxidize in the air.
• High levels of Carbonate appear on reactive metal oxides and various hydroxides.  This is due to reaction between the oxide and CO₂ in the air.
• Hydroxide contamination peak is due to the reaction with residual water in the lab air or the vacuum.
• The O (SO) BE of the hydroxide (water) contamination normally appears 0.5 to 1.0 eV above the oxide peak
• Potassium (K), Potassium (K), Sulfur (S) and Chlorine (Cl) are common trace to low level contaminants
• To find low level contaminants it is very useful to vertically expand the 0-600 eV region of the survey spectrum by 5-10X
• A tiny peak that has 3 or more adjacent data-points above the average noise of the background is considerate to be a real peak
• Carbides can appear after ion etching various reactive metals.  Carbides form due to the residual CO and CH₄ in the vacuum.
• Ion etching can produce low oxidation states of the material being analyzed.  These are newly formed contaminants.
• Ion etching polymers by using standard Ar+ ion guns will destroy the polymer, converting it into a graphitic type of carbon

→  Periodic Table 

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Data Collection Guidance

• Chemical state differentiation can be difficult
• Long time exposures (high dose) to X-rays can degrade various polymers, catalysts, high oxidation state compounds
• During XPS analysis, water or solvents can be lost due to high vacuum or irradiation with X-rays or Electron flood gun
• Auger signals can sometimes be used to discern chemical state shifts when XPS shifts are very small

→  Periodic Table 

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Data Collection Settings for K (2p_3/2)

• Conductivity:  Metal readily develops a native oxide that is sensitive to Flood Gun – Differential Charging Possible – float sample recommended
• Primary Peak (XPS Signal) used to measure Chemical State Spectra:  K (2p_3/2) at 294 eV
• Recommended Pass Energy for Measuring Chemical State Spectrum: 50-60 eV    (Produces Ag (3d_5/2) FWHM ~0.7 eV)
• Recommended # of Scans for Measuring Chemical State Spectrum:  4-5 scans normally   (Use 10-25 scans to improve S/N)
• Dwell Time:  50 msec/point
• Step Size:  0.1 eV/point   (0.1 eV/step or 0.1 eV/channel)
• Standard BE Range for Measuring Chemical State Spectrum:  288 – 318 eV
• Recommended Extended BE Range for Measuring Chemical State Spectrum:  275 – 355 eV
• Recommended BE Range for Survey Spectrum:  -10 to 1,100 eV   (above 1,100 eV there are no useful XPS signals, except for Ge, As and Ga, above 1100 is waste of time)
• Typical Time for Survey Spectrum:  3-5 minutes for newer instruments, 5-10 minutes for older instruments
• Typical Time for a single Chemical State Spectrum with high S/N:  5-10 minutes for newer instruments, 10-15 minutes for older instruments  

→  Periodic Table 

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Effects of Argon Ion Etching

• Carbides can appear after ion etching various reactive metals.  Carbides form due to the residual CO and CH₄ in the vacuum.
• Ion etching can produce low oxidation states of the material being analyzed.  These are newly formed contaminants.
• Ion etching polymers by using standard Ar+ ion guns will destroy the polymer, converting it into a graphitic type of carbon

 

→  Periodic Table 

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